OMV extra - plexmediaserver plugin not found

I have followed the omv extra guide to install plex via the repo in omv extra, omv extra installed is openmediavault-omvextrasorg_latest_all4.deb, however when I enable the plex repo the page does not apply the settings. Checking in the plugins results in no plexmediaserver plugin being found.

It was suggested to use docker instead, but the same issue happens when trying to install the docker plugin via the Docker CE repo.

It was suggested that this could be related to a DNS issue, however I am able to ping google.com.

When running apt-get update i get the following output there are a lot of Ign:

Towards the end of this output there it seems that some server certificate fails: -

Do you have any further insights into a resolution for this issue? Is this cert issue only apparent on OMV 4.x?

As I mentioned before, I don't know what causes this or how to fix it. It is not an OMV issue. It just affects some Debian and Ubuntu systems. You could search the web more but most of the suggestions on how to fix do not fix it.